This back extension exercise is sometimes called the Superman, and works your lower back. You start this exercise by laying face down on a mat and stretching your arms in front of you as if you were Superman flying. Tighten your abs and lift your head and chest off the floor, but keep your feet in touch with the ground. Lower your head and chest back to the starting position. Remember to keep your neck and spine aligned during this exercise, and don't extend your head more than 8 to 12 inches.